Since electric-power converting devices using switching of power semiconductor elements have high conversion efficiency, the electric-power converting devices are widely utilized for commercial uses, mounting in cars, railroads, electric transformation equipment, etc. Since this power semiconductor element generates heat when electricity is distributed, high heat dissipation performance is required. Normally, in heat dissipation, a metal-made heat dissipating structure having fins is used, and it is grounded to the ground (GND) in order to stabilize electric potentials and to prevent electric shock. Therefore, an insulating material disposed between the power semiconductor element and the heat dissipating structure is required to have excellent thermal conductivity. However, if the voltage to be converted is high, the insulating material has to be formed to be thick in order to improve insulating performance, and heat dissipation performance is deteriorated.
As a method of improving the heat dissipation performance, a method of sandwiching a conductor, which is a highly thermally conductive material, between an insulating layer and an insulating layer for example as shown in PTL 1 is known.